Method of manufacturing permanent magnets having large coercive force



1965 HAKARU MASUMOTO ETAL 3,211,592

METHOD OF MANUFACTURING PERMANENT MAGNETS HAVING LARGE COERCIVE FORCE Filed April 16, 1963 3 Sheets-Sheet 1 Alco IZOO- L+8 HOO- IOOO

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METHOD OF MANUFACTURING PERMANENT MAGNETS HAVING LARGE COERCIVE FORCE Filed April 16, 1963 3 Sheets-Sheet 3 450C I 500C 032.52 o com 3 ATTORNEY United States Patent Ofilice 3,211,592 Patented Oct. 12, 1965 facturing permanent magnets consisting of 75 to 90% Co, 10 to 25% Al and a small quantity of impurities.

nets were known where they are compressed iron powder magnets, compressed Fe-Co powder magnets, Bismanol (Mn-Bi alloys), Ferroxdure (BaO.6Fe O etc. which have pretty large residual flux density (Br) and coercive force (He). netic powders of very fine and adequate size should be prepared and then compressed with a suitable pressure. Some of them should be sintered further at high temperatures, more particularly, in the former two magnets it is extremely difiicult to prepare fine particles of a desired size and the method of manufacturing is pretty complicated. nets is usually very complicated and difiicult and moreover, almost impossible to always obtain the product of the same characteristics.

METHOD OF MANUFACTURING PERMANENT MAGNETS HAVING LARGE COERCIVE FURCE Hakarn Masumoto, Sendai, Taken Kobayashi, Kozuka- 5 The present invention relates to a method of manu- The principal object of the invention is to provide permanent magnets having a large coercive force.

Heretofore single magnetic domain fine particle mag- In the manufacture of these magnets mag- In other words, the manufacture of such mag- In order to overcome the above described difiiculties the The invention will be explained with reference to the accompanying drawings, in which FIG. 1 represents the equilibrium diagram for Co-Al alloys;

FIG. 2 shows curves obtained by plotting the values in the characteristic table for illustrating the relation between the magnetic properties and composition of alloys tested by the inventors;

FIG. 3 shows curves illustrating the relation between pering time for three kinds of alloys, E, F and G in the Table; and

FIG. 4 illustrates demagnetizing curves of the alloys E, F and G.

After the results of various investigations, the inventors have ascertained that the equilibrium diagram of Co-Al alloys as shown in FIG. 1 is adapted to such a condition, that is, referring to FIG. 1, Co-Al alloys containing 10 to 26% Al exhibit a single phase of substantially 6 solid solution at room temperature if rapidly cooled from a temperature of 6 phase range or a temperature above the eutectic line, or if cast in a metal or sand mold, but if Co-Al alloys containing '10 to 26% Al are heated to a suitable temperature below ab solid solution line for a suitable time, single magnetic domain fine particles of 5 phase are precipitated,

Now the results of investigations made by the inventors will be explained in detail.

At first, in order to manufacture the alloy of the invention a suitable amount of cobalt is melted in a suitable melting furnace in air or in vacuo and then to remove gases a small amount of Mn, Si, Al, Ti and other degassing agents are added and then a suitable amount of Al is added and thoroughly agitated to provide a fused alloy having uniform composition. Then the molten alloy is poured in a mold of a suitable shape and size to provide a sound ingot or product. A forgeable product according to the composition is forged at a suitable high temperature to obtain a product of a desired shape.

Then the cast or forged article thus obtained is quenched in water, oil, air or other suitable medium from a suitable temperature above ab solid solution line or eutectic line shown in FIG. 1 to form its greater part as 5 solid solution, through the optimum cooling speed is suitably selected according to the composition of the particular alloy. Then the product is heated at a suitable temperature below the ab solid solution line but within the region of 6+ for a suitable time to temper. For a particular alloy, when it is cast in a metal mold or sand mold, the said tempering treatment is applied to it without any solid solution treatment. Thus the single magnetic domain fine particles of phase is precipitated in the non-magnetic matrix of e. The product thus obtained is magnetized in a strong magnetic field, then a permanent magnet is obtained having very high coercive force such as 1320 oersted (0e) at the maximum.

Various heat treatments are subjected to 13 kinds of alloys made by melting in air and among the results of experiment the properties of alloys having largest coercive the magnetic properties, tempering temperature and temforce are shown in the following table.

TABLE Composition (percent) Mark of Treatment Br(G) Hc(Oe) (BHLML Density Remarks alloys (X10 90.3 9. 7 (b)500 0., 2 hrs. tempered 3. 200 87 Forgeable. 89. 5 10. 5 (b)550 0., 2 hrs. tempered 6,000 400 Do. 88. 7 11.3 (b)550 0., 3 hrs. tempered 6, 000 600 1. 40 Do. 87. 8 12. 2 )-500 0., 4 hrs. tempered 5, 700 800 2.02 Do. 87.4 12. 6 (a)550 0., 3 hrs. tempered 4,600 950 1. 51 D0. 87. 4 12. 6 (b)500 0., 16 hrs. tempered 5, 600 870 2.02 Do. 87. 4 12. 6 (c)-550 0., 4 hrs. tempered 5,000 450 0.78 Do. 86. 4 13.6 (a)500 0., 24 hrs. tempered 4, 600 920 1. Somewhat untorgeable. 86. 4 13. 6 (b)550 0., 4 hrs. tempered 4, 800 1,050 2. 11 Do. 86.4 13. 6 (c)550 0., 4 hrs. tempered 4,000 650 0. 99 D0. 85. 4 14.6 (a)550 0., 3 hrs. tempered 4,100 1,050 1. 70 Do. 85.4 14.6 (b)550 0., 4 hrs. tempered 4, 300 1, 320 2. 38 Do. 85.4 14.6 (c)550 0., 4 hrs. tempered 4, 500 1,000 1. 76 Do. 83.4 16. 6 (b)-550 0., 3 hrs. tempered 3, 800 1, 310 2.03 Almost un- Iorgeable. 80.4 19. 6 (b)500 0., 16 hrs. tempered 2,400 1,200 1.00 Do. 78.4 21. 6 d0 1, 500 800 0.45 Do. 76. 5 23. 5 o 1, 200 500 0.27 Do. 75. 5 24. 5 (b)-500 0., 10 hrs. tempered.- 700 300 Do. 74. 5 25. 5 (b)500 0., 10 hrs. tempered 500 100 Do.

Treatments:

(a)Aiter casting in an iron mold. (b)After quenched in water from 1,375 0.

(c)After quenched in air irom 1,375 0.

Thus, it will be seen that by changing the extent of solution treatment, quenching speed tempering temperature and duration etc. various magnetic properties different from those described in the table can be obtained.

FIG. 2 illustrates curves showing the relation between the magnetic properties and composition of the alloy which is quenched in water from 1375 C. and then tempered. Thus it will be apparent from the above table and FIG. 2 that a very large coercive force can be obtained by a simple method of manufacturing alloys and its heat treatment.

From the curves in FIG. 2 we can further obtain the following relation:

Al I Br(G) l Hc(Oe) Accordingly all of the Co-Al alloys Within the range of 75-90% of Co and 25-10% of Al; 77-89.5% of Co and 23-10.5% of Al; 80-88% of Co and 2012% of Al; and 82-86% of Co and 18-14% of Al can develop the desired properties according to the heat treatment of the invention.

Next, FIGQB illustrates the magnetic properties of three kinds of alloys, E, F and G which are tempered at various temperatures for different times, ie that the maximum coercive force is obtained by tempering at 550 C. for 4 hours.

FIG. 4 illustrates the demagnetization curves of the three kinds of alloys E, F and G.

As apparent from the above table, the Co-Al alloys containing 9.7 to 12.6% Al is forgeable at high temperatures, yet when A1 is increased the forging becomes somewhat difficult, and when Al attains higher than 16.6% the forging becomes substantially impossible. These alloys have a low specific gravity as they contain Al.

In short, according to the method of the invention, the alloy containing 75 to 90% Co, 10 to 25% Al and a small amount of impurities is chill cast in a mold or quenched from a high temperature above the solid solution line or eutectic line by a suitable process to make solid solution, then it is tempered at a suitable temperature below the solid solution line or eutectic line, or for some alloys the cooling speed is suitably slowed down when the alloy is cast in a metal mold or sand mold,

or when quenched in a suitable medium after it has been treated to cause said solid solution, this tempering or heating being conducted within the e+ binary region to precipitate a single magnetic domain fine particle of g in the non-magnetic matrix of e, thereby enabling the development of a very large coercive force such as 1320 Oe and the residual flux density substantially larger than that of ferrite magnets. Accordingly, the method of the invention is specially adapted for the manufacture of short magnets. And the alloys of the invention have the particularity of enabling forging according to the composition and have pretty small specific gravity.

What we claim is:

1. A method of manufacturing high coercive force permanent magnets, comprising heating an alloy consisting essentially of about -90% cobalt and about 25-10% aluminum to a temperature above the 5+ binary region,

.' quenching the alloy to a temperature below the upper boundary of the 5+ binary region, heating the alloy in said binary region at a temperature sufficient to precipitate fine particles of ferromagnetic g in a matrix of nonmagnetic e, and magnetizing the product thus obtained in a strong magnetic field to obtain a permanent magnetic having high coercive force.

2. A method as claimed in claim 1, in which said alloy consists essentially of about 77-89.5% cobalt and about 23-10.5% aluminum.

'3. A method as claimed in claim 1, in Which said alloy consists essentially of about 80-88% cobalt and about 20-12% aluminum.

4. A method as claimed in claim 1, in which said alloy consists essentially of about 82-86% cobalt and about 18-14% aluminum.

5. A method as'claimed in claim 1, in which said temperature is above about 350 C.

References Cited by the Examiner UNITED STATES PATENTS 2,082,041 6/37 Williams 148-102 FOREIGN PATENTS 342,868 2/31 Great Britain.

OTHER REFERENCES Basic Metallurgy, published by the A.S.M., edited by A. W. Grosvenor, 1955, pp. 498-517.

Constitution of Binary Alloys by Hansen 2nd edition, McGraw-Hill Book Company (pages 79-81 relied upon).

Metals Handbook, 1948 edition, pp. 11 and 1158.

DAVID L. RECK, Primary Examiner. 

1. A METHOD OF MANUFACTURING HIGH COERCIVE FORCE PERMANENT MAGNETS, COMPRISING HEATING AN ALLOY CONSISTING ESSENTIALLY OF ABOUT 75-90% COBALT AND ABOUT 25-10, ALUMINUM TO A TEMPERATURE ABOVE THE E+$ BINARY REGION, QUENCHING THE ALLOY TO A TEMPERATURE BELOW THE UPPER BOUNDARY OF THE E+$ BINARY REGION, HEATING THE ALLOY IN SAID BINARY REGION AT A TEMPERATURE SUFFICIENT TO PRECIPITATE FINE PARTICLES OF FERROMAGNETIC $ IN A MATRIX OF NONMAGNETIC E, AND MAGNETIZING THE PRODUCT THUS OBTAINED IN A STRONG MAGNETIC FIELD TO OBTAIN A PERMANENT MAGNETIC HAVING HIGH COERCIVE FORCE. 